The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
Aspects of the present invention relate to a butterfly valve, comprising a housing including a passageway defined by an internal surface of the housing, said passageway having a center line in axial direction thereof, a valve seat enclosing the passageway, a valve shaft rotatably mounted to the housing and having an axis of rotation extending through the center line and spaced from a plane through the valve seat, a valve plate member fixed to the valve shaft and being located in the passageway, a seal enclosing the valve plate member, said valve plate member having an open position and a closed position, in which the seal is in engagement with the valve seat so as to close the passageway.
An earlier butterfly valve of the applicant was designed for filling and/or emptying containers for storage of liquid material, for example. This type of butterfly valve has a valve plate member, wherein the valve plate member is provided with a circular disc which is enclosed by a sealing ring. The valve shaft is eccentrically fixed to the disc and located at one side thereof. The passageway is closed by the sealing ring in the closed position. This configuration makes the valve suitable for use in storing sterilized liquids in the container as infections cannot penetrate from the outside into the liquid through narrow spaces between the valve shaft and the housing such as is the case in well-known butterfly valves having a valve shaft through the center of the disc. However, a disadvantage of the butterfly valve with an eccentrically positioned valve shaft is that it is sensible to leakage just after closing the butterfly valve as a consequence of temporary deformation of the seal near the valve shaft when the valve plate member is in the open position.